code: def downgrade():
      pass
  
file_path: mlflow/mlflow/store/db_migrations/versions/90e64c465722_migrate_user_column_to_tags.py
imports: from alembic import op
  import sqlalchemy
  from sqlalchemy import orm, Column, Integer, String, ForeignKey, PrimaryKeyConstraint
  from sqlalchemy.orm import relationship, backref, declarative_base
  from mlflow.utils.mlflow_tags import MLFLOW_USER
label_desc: Use image node_id 2 for calling a global function with example usage: downgrade() without return types